Several models will be used to analyze the ontogeny and phylogeny of immunocompetent cells. Four major areas related to ontogeny of immunologic effector cell activity will be examined to: 1) test immunologic functional changes in different age classes of cyprinodont fish; 2) determine if the function of amphibian bone marrow is similar to that of mammals; 3) establish the immunocompetence and potentiality of BM lymphoid cells in the T-cell response; 4) analyze Con A and PHA responses in pre-, post-metamorphic and young (SVL less than or equal to 40 mm; 50-70 mm) Rana pipiens, completing the picture on the ontogeny of lectin responses. Regarding phylogeny and using enriched coelomocyte populations from earthworms, we will investigate the functions of each cell type and their surface properties. To elucidate the role temperature plays in regulating ectothermic immunity and mitogenesis, several interrelated areas will be investigated using Rana pipiens: a) Role of temperature on the generation of Con A and PHA secondary (memory) lymphocytes in vitro; b) use of T-independent (PVP), T-dependent (SRBC) and carrier hapten (DNP-LPS) antigens in conjunction with temperature manipulation to determine which cell population(s) are temperature-sensitive in vivo; c) temperature effects on the generation of immunological memory in vivo. All the results, taken together, suggest that T-cell progenitors evolved early in phylogeny and that certain lymphoctye characteristics have remained unchanged since the first vertebrates evolved.